Biological monitoring of exposure to monochlorobenzene.

We assessed the exposure to monochlorobenzene (MBC) of 44 male subjects performing maintenance work in a diphenylmethane-4-4'diisocyanate producing plant. In total, 251 whole shift personal air sampling measurements (passive diffusion) were carried out and at the end of the shift, during which the time-weighted average exposure (TWA) to MCB was determined, a urine sample was collected for the analysis of 4-chlorophenol and 4-chlorocatechol, the two main urinary metabolites of MCB in human. The MCB-TWA values were log normally distributed with a median of 1.2 ppm and a range from less than 0.05 to 106 ppm. The Pearson's correlation coefficient between the log MCB-TWA (ppm) and the log concentration (mg/g creatinine) of the metabolites in post shift-urine samples amounted to 0.65 (P less than 0.001) for 4-chlorophenol (log 4-chlorophenol = 0.22 + 0.43 log MCB-TWA) and 0.72 (P less than 0.001) for 4-chlorocatechol (log 4-chlorocatechol = 0.53 + 0.58 log MCB-TWA), respectively. On the average the workers excreted three times more 4-chlorocatechol than 4-chlorophenol. The follow up of 21 workers over several days did not show any tendency for the metabolite concentration in urine to increase during the workweek.